Mechanical advantage drive system for cycles

ABSTRACT

A cycle with a mechanical advantage drive system comprises a frame with at least one wheel rotationally attached to the frame. A drive rim is attached to the wheel adjacent to the outer circumference of the wheel. A pulley is rotationally attached to the frame. A belt is trained around and engages both the pulley and the drive rim. As a rider pedals to turn a crank arm adapted to drive the pulley, the pulley drives the belt, which in turn drives the wheel. Because the belt is positioned at the outer circumference of the wheel, an instantaneous fixed point along the lower side of the belt is created by the friction between the wheel and the surface along which the cycle travels. By passing the belt around the pulley, a mechanical advantage is created that significantly reduces the amount of force required on the belt to propel the cycle.

BACKGROUND OF THE INVENTION

In many regions of the world, cycles, for example, bicycles or tricyclesare still the predominant mode of transportation other than walking. Dueto depressed economic conditions, automobiles and the fuel to run themare simply not within the budget of the average person. Cycles are usedto carry loads including livestock, agricultural products, other wares(e.g., in baskets, panniers, on platforms, or in wagons or trailerspulled by the cycles), and even people as passengers (e.g., tricyclerickshaws). Further, even in wealthier regions of the world, theincreased cost of fuel, traffic congestion, and limited parking may makecycling a desired mode of commuter transportation in densely populatedareas. Cycles are also used heavily for exercise and recreation in moreaffluent regions as well.

Several forces resist the forward motion of a cycle, for example, abicycle or a tricycle. A first force is gravity when a rider propels acycle up an incline. A second force is friction between the cycle andthe surface along which the cycle travels. A third force is windresistance created by the forward motion of the cycle, blowing wind, orboth. Improvements to cycling technology that reduce the effort of arider to propel a cycle would likely significantly benefit riders ofcycles in any of the potential uses described above.

The information included in this Background section of thespecification, including any references cited herein and any descriptionor discussion thereof, is included for technical reference purposes onlyand is not to be regarded subject matter by which the scope of theinvention is to be bound.

SUMMARY

The mechanical advantage drive system for cycles disclosed herein takesadvantage of the second frictional force to reduce the force necessaryfor exertion by a rider to overcome the first force of gravity. Further,because the force required of the rider is reduced, an ability to haul aload of greater mass is provided. This provides an opportunity to addfairings or other aerodynamic structures to the cycle because theadditional force needed to propel the cycle with the added weight of thefairings is reduced by the mechanical advantage of the drive system. Ifthe cycle were equipped with fairings, the force of wind resistanceagainst the cycle and rider could also be reduced, again reducing theforce required by the rider to propel the cycle.

In one implementation, a cycle with a mechanical advantage drive systemcomprises a frame with at least one wheel rotationally attached to theflame. A drive rim is attached to the wheel adjacent to the outercircumference of the wheel. A pulley is rotationally attached to theframe. A belt is trained around and engages both the pulley and thedrive rim. A crank arm is rotationally attached to the frame and adaptedto drive the pulley as the rider pedals to turn the crank arm. In thismanner the belt drives the wheel when the crank arm drives the pulley.Because the belt is positioned at the outer circumference of the wheel,an instantaneous fixed point along the lower side of the belt is createdby the friction between the wheel and the surface along which the cycletravels. By passing the belt around the pulley, a mechanical advantageis created that significantly reduces the amount of force required onthe belt to propel the cycle. If the pulley effect was ideal, the forcereduction would be one half the force otherwise required to propel thecycle against the force of gravity.

In another implementation, a bicycle with a mechanical advantage drivesystem comprises a frame with front and rear wheels rotationallyattached to the frame. A drive rim is attached to the rear wheeladjacent to an outer circumference of the rear wheel. A pulley isrotationally attached to the frame and positioned behind the rear wheel.A belt is trained around and engages both the pulley and the drive rim.A crank arm is rotationally attached to the frame and adapted to drivethe pulley as the rider pedals to turn the crank arm. In this manner thebelt drives the rear wheel when the crank arm drives the pulley. Thepulley system may be used in conjunction with a standard drive systemfor the bicycle wherein a chain ring drives a sprocket or cassette onthe hub of the rear wheel. Through the use of a freewheel in both thehub of the rear wheel and in the mounting of the pulley to the frame,the gearing of the bicycle can be designed to allow the mechanicaladvantage drive system of the pulley to overtake the standard drivesystem when the standard drive system is in its lowest gear.

In a further implementation, a tricycle with a mechanical advantagedrive system comprises a frame with a front wheel and two rear wheelsrotationally attached to the frame. A drive rim is attached to the frontwheel adjacent to an outer circumference of the front wheel. A pulley isrotationally attached to the frame and positioned behind the frontwheel. A belt is trained around and engages both the pulley and thedrive rim. A crank arm is rotationally attached to the frame and adaptedto drive the pulley as the rider pedals to turn the crank arm. In thismanner the belt drives the rear wheel when the crank arm drives thepulley. Through the use of a freewheel in both the hub of the frontwheel and in the mounting of the pulley to the frame, the gearing of thetricycle can be designed to allow the mechanical advantage drive systemof the pulley to overtake the primary drive system when the primarydrive system is in its lowest gear. The frame of the tricycle may becomposed of a front portion, an interface portion, and a rear portion,wherein the front portion is attached to the front wheel, the interfaceportion is rotationally attached to the front portion, and the rearportion is hinged to the interface portion and attached to both thefirst rear wheel and the second rear wheel.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Otherfeatures, details, utilities, and advantages of the claimed subjectmatter will be apparent from the following more particular writtenDetailed Description of various embodiments and implementations asfurther illustrated in the accompanying drawings and defined in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of two equal masses at rest, a first tobe lifted directly and a second to be lifted using the mechanicaladvantage of a pulley.

FIG. 1B is a schematic diagram of the masses of FIG. 1 indicating themechanical advantage in lifting the masses achieved through the use ofthe pulley.

FIG. 2 is a schematic diagram of the concept of mechanical advantage ofa pulley applied to a bicycle wheel.

FIG. 3 is a right elevation view of a rear wheel drive bicycleimplementing a mechanical advantage pulley drive system.

FIG. 4 is an isometric detail view of the front wheel and drive rim ofthe bicycle of FIG. 3.

FIG. 5 is an exploded view of the front wheel and drive rim of FIG. 4.

FIG. 6 is a front isometric view of a front wheel drive tricycleimplementing a mechanical advantage pulley drive system.

FIG. 7 is a rear isometric view of the front wheel drive tricycle ofFIG. 6.

FIG. 8 is a right elevation view of the tricycle of FIG. 6.

FIG. 9 is a left elevation view of the tricycle of FIG. 6.

FIG. 10A is an enlarged view of the area indicated in FIG. 6 detailing asteering mechanism of the tricycle.

FIG. 10B is a cross section view in the plane indicated in FIG. 10A of ahinged attachment structure between the rear wheel forks and the handlebar of the tricycle of FIG. 6.

FIG. 11 is a left elevation view of a second embodiment of a front wheeldrive tricycle implementing a mechanical advantage pulley drive system.

DETAILED DESCRIPTION OF THE INVENTION

A corollary to the law of conservation of energy is that the mechanicalenergy of a closed system remains constant. Pulley systems that providea mechanical advantage must obey this conservation law. For example,although a pulley system can be used to reduce the force required tolift a mass by one-half or more, there is a tradeoff in that the rate atwhich the pulley system operates to lift the mass is also halved. Thegoal of the mechanical advantage drive system for cycles describedherein is to similarly reduce the force necessary for a cyclist toimpart to propel a cycle up an incline. However, because cycles aregenerally geared to provide easier pedaling with a consequent reductionin speed, gearing options may be selected for mechanical advantage drivesystem for cycles such that there is no reduction in the speed of thecycle compared to standard gearing systems, while still providing thebenefit of mechanical advantage.

FIG. 1A depicts two equal masses, a first mass 102 and a second mass 106at rest on a surface 114. The first mass 102 is attached to a cable 104with which the first mass 102 may be lifted from the surface 114.Alternatively, the second mass 106 is attached to a pulley 108, throughwhich is threaded a cable 110 with which the second mass 106 may belifted from the surface 114. A first end of the cable 110 a is affixedto a fixed support 112. A second end of the cable 110 b is free and isused to exert a pulling force to lift the second mass 106 as furtherdepicted in FIG. 1B.

The masses are shown in positions of being lifted in FIG. 1B. A force Fis exerted on the cable 104 in order to lift the first mass 102 from thesurface 114. The force F is at least the minimum necessary force toovercome an opposing force F′ on the first mass 102 due to gravity,i.e., F>F′. Similarly, an upward force is exerted on each end of thecable 110 attached to the second mass 106 via the pulley 108. When apulling force ½ F is exerted on the second end of the cable 110 b, andequal upward pulling force ½ F is exerted on the pulley via the firstend of the cable 110 a attached to the fixed support 112. Assuming forthe sake of example that the pulley has no mass, the combination offorces ½ F is at least the minimum necessary force to overcome anopposing force F′ on the second mass 106 due to gravity, i.e., ½ F+½F>F′.

Thus, as indicated schematically in FIG. 1B, the pulley 108 provides amechanical advantage in lifting the second mass 106 from the surface114. An applied force F is required to lift the first mass 102, but anapplied force of only ½ F is needed to lift the equal second mass 106.This advantage occurs because the pulley 108 allows the first end of thecable 110 a to be attached to the fixed support 112, which bears half ofthe weight of the second mass 106. Thus, the mechanical advantagegenerated is 2:1. Additional mechanical advantage can be created byrouting the cable through one or more additional pulleys attached to thefixed support and the second mass.

Note, that there is a trade-off in achieving such mechanical advantage.As shown in FIG. 1B, the first mass 102 is lifted a distance D from thesurface 114 upon application of the force F over a period of time.However, the second mass 106 is only lifted a distance ½ D from thesurface 114 upon application of the force ½ F over the same period oftime. Thus, for each incremental increase in the mechanical advantageratio, there is an equal decrement in the distance traveled by a mass.

This concept of mechanical advantage is translated to a cycle, either abicycle or a tricycle as described herein (although the concept could betranslated to any form of wheeled vehicle with any number of wheels). Asshown in FIG. 2, a wheel 202 of a cycle 200 is in contact with a surface220, for example, the ground or a road. (Note that only a single wheeland drive system of the cycle 200 are shown in FIG. 2 for clarity,simplicity, and comparison with the mechanical advantage conceptsdepicted in FIG. 1B.) As with most human powered cycles, a chain ring206 is rotated by a rider whose feet and legs push pedals 210 attachedto the chain ring 206 via crank arms 208 in a circular motion.

In the implementation of FIG. 2, the chain ring 206 drives a transferring 214 via a chain 212 as opposed to driving the hub of the wheel,which is the normal operation of a cycle. The transfer ring 214 is fixedto a pulley 216, thereby transferring the rotational motion imparted bythe rider on the chain ring 206 to the pulley 216. The pulley 216 inturn drives the wheel 202 via a belt 218 that engages a drive rim 204adjacent the circumference of the wheel 202.

As depicted in FIG. 2, the cycle 200 is opposed by a combined force F′of gravity and friction between the cycle 200 and the surface 220 thatimpedes the forward motion of the cycle 200. At any given time, eitherat rest or in motion, the wheel 202 of the cycle 200 is in constantcontact with the surface 220 at contact point 222. This contact point222 may be viewed as similar in function to the fixed support 112 inFIGS. 1A and 1B. The belt 218 driving the wheel 202 is constantlypositioned adjacent the contact point 222 as the wheel 202 rotates.Thus, the belt 218 can be considered as being constantly,instantaneously fixed at the contact point 222.

The force exerted by a rider on the pedals 210 is translated into alinear motion of the chain 212 in a generally forward direction asindicted by the arrow A. The forward linear motion of the chain 212 isfurther translated into generally forward linear motion of the belt 218by the pulley 216. Translating the mechanical advantage concepts of FIG.1B to the cycle 200 of FIG. 2, it can be seen that a force approximatelyequal to ½ F on a top portion of the belt 218 a is sufficient to movethe cycle 200 forward along the surface 220, where ½ F+½ F≈F′. Thisresults because a bottom portion of the belt 218 b similarly exerts aforce approximately equal to ½ F translated across the belt 218 by thepulley 216 pulling the bottom portion of the belt against the contactpoint 222. The contact point 222 provides resistance force on the bottomportion of the belt 218 b due to the weight of the cycle and the rideron the wheel 202 at the interface with the surface 220 and the frictionthere-between.

In FIG. 2 the crank arm 208 and pedal 210 are depicted as attached to achain ring 206 which in turn drives the pulley 216 via the chain 212.This arrangement mimics the arrangement of components on a traditionalbicycle for driving a rear wheel. In particular, the use of a chain andchain ring on a bicycle allow the pedals to be conveniently positionedfor pushing by the rider while driving the rear wheel while providing anergonomically efficient position for the rider, generally balanced onthe frame between the front and rear wheels. The chain and chain ringfurther provide an ability to shift between multiple gears usingsprocket cassettes and derailleur configurations.

However, it should be apparent in FIG. 2 that the same mechanicaladvantage could be achieved in driving the wheel 202 if the crank armswere directly driving the pulley 216. In such a configuration, the frontwheel of a cycle may be driven with or without linkage between the crankarms and an intermediate chain ring and chain. Further, the use ofcomponents such as a Speed Drive® (Schlumpf Innovations, Switzerland),an epicyclic gear system built into the crank set, in a hub of thepulley may allow for direct gearing alternatives when driving the pulleydirectly with the crank arms.

The diameter of the chain ring 206 may need to be larger than a chainring of a normal bicycle. The diameter of the chain ring 206 is relatedto the diameters of the drive rim 204 on the wheel 202 and the pulley216. Because the diameter of the pulley 216 is less than the diameter ofthe drive rim 204 and both are connected by the belt 218, the diameterof the chain ring 206 must be longer than on a normal bicycle tocompensate. Another option to avoid a diameter increase in the chainring 206 is to incorporate a Speed Drive in the crank set as describedto provide the needed gearing.

The mechanical advantage imparted to a cycle as depicted in FIG. 2 isimplemented in the form of a bicycle 300 as depicted in FIG. 3. Thebicycle 300 is generally of typical construction including a front wheel302 and a rear wheel 304 attached to a frame 316. Both the front wheel302 and the rear wheel 304 are constructed of a rim 308 a, 308 b thatsupports a tire 306. Each rim 308 a, 308 b is attached to a respectivehub 312, 314 in the center of the wheels 302,304 by a plurality ofspokes 310. The rear hub 314 generally includes a freewheel assembly toallow the bicycle 300 to coast when the rider is not pedaling or thebicycle 300 is moving faster than the rider can pedal.

The frame 316 primarily comprises a top tube 318, a head tube 320, adown tube 322, a seat tube 324, and a bottom bracket 326. The top tube318 and the down tube 322 are both joined at one end to the head tube320. The opposite end of the top tube 318 is joined to one end of theseat tube 324. The opposite end of the seat tube 324 is with the bottombracket 326 as is the second end of the down tube 322. This embodimentof the frame 316 as depicted is typical of most standard bicycles.However, it should be understood * that the mechanical advantage drivesystem described herein may be implemented with any frame design orstructure, for example, fully suspended mountain bike frames and otheradvanced frame designs.

A front fork 328 extends from the head tube 320 on each side of thefront wheel 302 where a fork dropout (not shown) in the front fork 328attaches to an axle (not shown) extending from the front hub 312. Achain stay 330 extends rearward from the bottom bracket 326 on each sideof the rear wheel 304 to the rear hub 314. Similarly, a seat stay 332extends rearward from the junction of the top tube 318 and the seat tube324 on each side of the rear wheel 314 and joins with the chain stay 330at the rear hub. The junction of the chain stay 330 and the seat stay332 form a rear dropout (not shown) that attaches to an axle 374 (notshown in FIG. 3; see FIG. 4) extending from the rear hub 314.

Note that the drawings herein should be considered schematic and thussome of the detail of cycle construction is not depicted for purposes ofclarity, although such details are well known in the art of cycledesign. For example, although braking systems are provided on mostcycles and would be incorporated into each embodiment of the cyclesdescribed herein, a braking system is not depicted to allow for aclearer depiction of the features of a mechanical advantage drivesystem. Similarly, gear shift levers, cables, and some derailleurs,although contemplated in the design and operation of the cyclesdescribed herein, are not depicted to provide additional clarity in thedepiction of other features of the cycles. The inclusion of suchadditional components and features are well known and it is well withinthe ordinary skill of cycle designers and mechanics to add suchadditional components to the cycles described herein.

A seat post 334 extends upward from the junction of the top tube 318 andthe seat tube 324 and supports a seat 336. The seat post 334 alsoextends within the seat tube 324 to allow for adjustment of the heightof the seat 336.

A stem 338 extends upward from the head tube 320 to support handlebars340. The stem 338 also extends within the head tube 320 to allow foradjustment of the height of the handlebars 340. The stem 338 is attachedto the front fork 328 and rotates within the head tube 320 to allow forsteering of the bicycle 300.

The drive system of the bicycle 300 is, in part, typical and starts witha pair of pedals 342 attached to a pair of crank arms 344 that extendfrom the bottom bracket 326. The crank arms 344 are attached to each endof a spindle (not shown) that rotates within the bottom bracket 326. Achain ring 346 is attached to one side of the spindle (the right side asshown in FIG. 3) or directly to the crank arm 344 on the right side. Thechain ring 346 thus rotates around the bottom bracket 326 as the riderpushes the pedals 342 in a circular motion.

The chain ring 346 has a plurality of teeth that extend from thecircumference of the chain ring 346. The teeth engage a chain 348, whichis a continuous loop that engages the rear hub 314 to drive the rearwheel 304. There may be more than one chain ring 346; two and threechain rings are commonly found on bicycles. A front derailleur (notshown) is generally used to transfer the chain 348 from one chain ringto another.

The chain 348 connects the chain ring 346 to one or more toothedsprockets on the rear hub 314. A plurality of sprockets, generallycollected and attached together as a cassette 350, is attached to therear hub 314 on the right side of the bicycle 300. The chain 348 engagesthe teeth of one sprocket in the cassette 350 at a time. The chain 348is also threaded through a rear derailleur 352 that moves the chain 348between the sprockets in the cassette 350.

The mechanical advantage drive system for the bicycle 300 iscomplementary to the standard drive system described above. Toaccommodate the additional components for the mechanical advantage drivesystem, the frame 316 is further composed of a pair of top pulley braces364 that extend rearward on each side of the rear wheel 304 from thejunction of the top tube 318 and the seat tube 324 and a pair of bottompulley braces 366 that extend rearward on each side of the rear wheel304 from the junction of the seat stay 332 and the chain stay 330. Eachtop pulley brace 364 is joined to a respective bottom pulley brace 366at a point behind the rear wheel 304. A pulley hub 362 is positionedbetween the junction of the top and bottom pulley braces 364, 366 and isattached thereto.

Returning to the bottom bracket 326, the left side of the spindle, theleft crank arm 344, or both may be attached to one or more transferrings 354 that are also driven by the rider pushing the pedals. Thetransfer ring 354 is toothed about the circumference similar to thechain ring 346. A second chain 356 engages the transfer ring 354 andextends rearward along the left side of the rear wheel 304 as acontinuous loop to drive the pulley hub 362. One or more sprocketsforming a pulley cassette 358 may be attached to the left side of thepulley hub 362. The second chain 356 engages the sprockets of the pulleycassette 358 to turn the pulley hub 362. A pulley derailleur 368 may beattached to the junction of the top and bottom pulley braces 364, 366and used to shift between the sprockets in the pulley cassette 358.

A pulley 360 is attached to the right side of the pulley hub 362. Thepulley 360 may thus be turned by rotational transfer from the pulleycassette 358 through the pulley hub 362. The circumference of the pulley360 is toothed to engage a belt 370 that is used to additionally drivethe rear wheel 304. A drive rim 372 is attached to the rim 308 b of therear wheel 304. The drive rim 372 is toothed and engages the belt 370driven by the pulley 360. The belt 370 may be made, for example, ofreinforced rubber or polymer, toothed on one side for engaging thepulley 360 and drive rim 372 and flat on the other to minimize potentialinterference with the ground or collection of dirt and grit due to theclose proximity of the belt 370 to the ground when traveling around therear wheel 304. Alternatively, the belt 370 may be a chain or othercontinuous loop of material capable of engaging the pulley 360 anddriving the drive rim 372.

FIGS. 4 and 5 depict the construction of the drive rim 372 in greaterdetail. The drive rim 372 may be attached to a sidewall of the rear rim308 b with a plurality of pins 378 inset into a plurality of respectiveapertures 376 in the sidewall of the rim 308 b. The pins 378 may be spotwelded or otherwise affixed to the apertures 376 in the rim 308 b. Thepins 378 provide a short separation distance between the drive rim 372and the rim 308 b to allow a measure of clearance between the belt 370and the rear wheel 304. Additionally, although not depicted, the driverim 372 may be supported by an additional set of spokes extending fromthe hub. In this configuration, the hub may be extended in lengthslightly on the side of the wheel of the drive rim 372 to provide spacefor attachment of the additional set of spokes.

The pulley hub 362 includes a freewheel allowing the pulley 360 to spinfreely as the rear wheel 304 rotates the pulley 360 via the belt 370faster than the gearing of the pulley cassette 362 is rotated by thepull of the second chain 356. The sprockets of the pulley cassette 358are geared such that freewheel in the pulley hub 372 spins freely whenall but the lowest gear combination of the cassette 350 on the rearwheel 304 and the chain rings 346 is engaged. The relationship betweenthe gears of the cassette 350 and the pulley cassette 358 is chosen suchthat the pulley 360 engages the rear wheel 304 when the second chain 356rotates the highest gear of the pulley cassette 358 at a faster speedthan the chain 348 rotates the lowest gear of the cassette 350. When thepulley 360 overtakes the cassette 350 as the drive for the rear wheel304, the freewheel in the rear hub 314 spins freely. The rear wheel 304is at this point driven by the belt 370 through engagement with thedrive rim 372.

The mechanical advantage achieved using the pulley 360 to drive the rearwheel 304 can be seen by comparing the configuration of the componentsof the bicycle 300 to the schematic diagram of the cycle 200 in FIG. 2.The belt 370 engaging the rear wheel 304 about the drive rim 372continuously passes a point adjacent to a surface on which the rearwheel 304 of the bicycle 300 is in contact. Thus, an instantaneous fixedpoint on the belt 370 is continuously achieved. When the pulley 360 isengaged, a mechanical advantage is achieved through the combination ofthe instantaneous fixed end of the belt 370 and the force transferacross the pulley 360, thus decreasing the force required of the rideron the second chain 356 to drive the belt 370 and move the bicycle 300forward.

The application of a mechanical advantage drive system to a cycle may beparticularly advantageous to tricycles. In many parts of the world,tricycles are still often used for hauling loads or passengers and thusburdened by significant weight that the rider must push. By providing adrive system that significantly decreases the force necessary to propelthe tricycle, the exertion required by a rider hauling a load issignificantly decreased. Alternately, the rider may be able to increasethe weight of the load he is able to carry.

An exemplary tricycle 400 implementation is depicted in FIGS. 6-10. Thetricycle 400 has a front wheel 404 a and two rear wheels 404 b, 404 cattached to a frame 413. Each of the wheels 404 a, 404 b, 404 ccomprises a hub 412 a, 412 b attached to a rim 408 a, 408 b, via a setof spokes 410. Tires 406 are mounted on each of the rims 408 a, 408 b.

A front portion 401 of the frame 413 is formed about a bottom bracket416, a front down tube 418, a seat tube 420, a pair of rear down tubes422 a, 422 b, and a pair of bottom tubes 424 a, 424 b. The front downtube 418 and the rear down tubes 422 a, 422 b are each attached at oneend to an upper portion of the seat tube 420. The lower end of the seattube 420 is fixed to the bottom bracket 416. The bottom tubes 424 a, 424b are attached at a first end to the bottom bracket 416 and at a secondend to the lower ends of the rear down tubes 422 a, 422 b. A pulley hub426 rotates on an axel mounted between the junction of the bottom tubes424 a, 424 b and the rear down tubes 422 a, 422 b.

The lower end of the front down tube 418 connects with an upper frontfork 414. A lower front fork 415 is connected at a first end to thebottom bracket 416 and extends forward to join the upper front fork 414and connect with and support an axle in the front hub 412 a about whichthe front wheel 404 a rotates. The junction of the front down tube 418and the upper front fork 414 may further be supported by a fork strut417 extending upward from the bottom bracket 416.

A head tube 428 interfaces with the seat tube 420 allowing the seat tube420 to turn on a bearing interface (not shown) within the head tube 428.The head tube 428 in this implementation, although located in anontraditional position, acts similar to a head tube in a bicycle tofacilitate steering of the tricycle 400 as further described below. Theseat tube 420 extends through the head tube 428 to support a seat 430. Aseat post (not shown) may fit within the seat tube 420 to allow theheight of the seat to be adjusted. A backrest bracket 432 may be fixedto either the bottom of the seat 430 or the top of the seat post to holda backrest 434 above and behind the seat 430 to support the back of arider.

A pair of angled handlebar brackets 436 a, 436 b is fixed to the headtube 428. The handlebar brackets 436 a, 436 b extend rearward at anglestoward the right and left sides of the tricycle 400, respectively. Inthis implementation, the handlebar brackets 436 a, 436 b form a trianglewith the head tube 428 such that the two open ends of the angle arefixed to the head tube 428 and the vertex of the angle is attached to ahandlebar 438.

As depicted, the handlebar 438 is generally a partial oval shape andextends from under the seat 430 to curve up and over the lap of a riderwhen seated in the seat 430 from each side of the tricycle 400. In thisconfiguration, the grips 439 of the handlebars 438 are available foreasy grasping by the rider to steer the tricycle 400 and aid in thebalance of the rider while on the tricycle 400. The head tube 428,handlebar 438, and handlebar brackets 436 a, 436 b function-as theinterface between the front portion 401 of the frame 413 and a rearportion 402 of the frame 413, connecting the rear wheels 404 b, 404 c tothe rest of the tricycle 400.

This interface also functions as the steering mechanism for the tricycle400, which is shown in greater detail in FIGS. 10A and 10B. A pair ofsuspension brackets 440 a, 440 b is fixed to the handlebar 438 adjacentthe handlebar brackets 436 a, 436 b, although the suspension brackets440 a, 440 b may be located elsewhere on the handlebar 438. Eachsuspension bracket 440 a, 440 b comprises a pair of plates between whicha hinge pin 472 is mounted. Two fork extensions 442 a, 442 b are mountedto a respective hinge pin 472 in each suspension bracket 440 a, 440 band extend rearward from the handlebar 438.

The rear wheels 404 b, 404 c are mounted to respective rear forks 444 a,444 b extending from each fork extension 442 a, 442 b. Each rear fork444 a, 444 b attaches to the axle of each rear hub 412 b. The rearwheels 404 b, 404 c are parallel and spaced evenly apart from a centralvertical plane of the front portion 402 of the frame 413. A basket,platform, bed, palette, pannier, or other load carrying structure (notshown) may be mounted to the rear portion of the frame 402 between therear wheels 404 b, 404 c to carry a load. A hitch (not shown) forattaching a trailer to pull a load may also or alternatively be mountedto the rear portion 402 of the frame 413.

An exemplary embodiment of one of the joints 474 a is shown in FIG. 10B.A cross tube 476 is formed in the fork extension 442 a through which thehinge pin 472 extends. The cross tube 476 is positioned adjacentthrough-holes in the suspension brackets 440 a. A bushing 482 may seatin each end of the cross tube 476. A bolt 478 is inserted into each ofthe through-holes in the suspension brackets 440 and extends into thecross tube 476. The bolts 478 are fastened to each end of the hinge pin472. The hinge pin 472 may be threaded on each end to allow bolts 478with internal threaded cavities to be tightened to each end of the hingepin 472. The outer walls of the bolts 478 that face the bushings 482 maybe tapered for interface with a set of roller bearings 480 interposedbetween the bolts 478 and the bushings 482. The roller bearings 480 maybe tapered to provide combined radial and thrust capacity for flexion ofthe joints 474 a, 474 b.

The front ends of the fork extensions 442 a, 442 b are also attached torespective ends of a restraint chain 470 that wraps around the seat tube420 below the head tube 428. The front ends of the fork extensions 442a, 442 b may have flanges 443 that extend downward (see FIG. 10A forgreater detail). The restraint chain 470 may be attached to the lowerends of these flanges 443. A head sprocket 468 is mounted at the top ofthe seat tube 420 and interfaces with the restraint chain 470. The headsprocket 468 may be formed of a toothed sprocket mounted on a set ofbearings that allow the head sprocket 468 to rotate around the seat tube420. In practice, the head sprocket 468 travels minimally as it isconstrained by its engagement with the restraint chain 470. However, theseat tube 420 may rotate within the head sprocket 468 on the bearings asthe seat tube 420 and the front portion 401 of the frame 412 and frontwheel are turned.

The restraint chain 470 also aids the hinge pins 472 in supporting thejoints 474 a, 474 b between the front portion 401 and the rear portion402 of the frame 413 and limits movement of the frame 413 about thehinge pins 472. The weight of the tricycle 400 and the rider thereonpush the joints 474 a, 474 b at the hinge pins 472 against the restraintchain 470. The restraint chain 470 thus prevents the fork extensions 442a, 442 b and rear wheels 404 b, 404 c from collapsing upward on thehinge pins 472 under the weight. A spring (not shown) may be used incombination with the hinge pins 472 to oppose an upward or downwardcollapse of the joints 474 a, 474 b about the hinge pins 472. Therestraint chain 470 does allow for slight flex and movement of the hingepins 472 during a turn as further explained below.

The greater the distance of the attachment point of the restraint chain470 on the flanges 443 from the hinge pins 472, the greater the lengthof the restraint chain 470 that moves around the head sprocket 468 fromone side of the tricycle 400 to the other. Stated another way, thegreater the radius of the attachment point of the restraint chain 470from the hinge pins 472 created by the flanges 443 results in a greaterarc length of movement of the restraint chain 470 when the joints 474 a,474 b flex about the hinge pins 272. The length of the flanges 443 andthe location of the head sprocket 468 on the seat tube 420 may becoordinated to orient the restraint chain 470 in various positions tochange the travel length of the restraint chain 270 and otherwise adjustthe interaction between rotation of the seat tube 420 within the headtube 428 and the flexion of the joints 474 a, 474 b.

A traditional steering system in which the front wheel 404 a is turnedis thus augmented to accommodate the drive system of the tricycle 400,which drives the front wheel 404 a. In the implementation shown in FIGS.6-10B, the tricycle 400 is steered by a combination of turning the seattube 420 within the head tube 428 and flexion of the joints 474 a, 474 bbetween the front portion 401 and rear portion 402 of the frame 413. Therider holds onto the handlebar 438 and, by rotating his body, the seat430, attached seat post 420, and thus the entire front portion 401 ofthe frame 413 turn with respect to the head tube 428 and the attachedrear portion 402 of the tricycle 400. Since the handlebar 438 and headtube 428 are attached to the rear wheels 404 b, 404 c, the handlebar 438and head tube 428 remain in a fixed frame of reference while the riderand front portion 401 of the tricycle 400 rotate.

Additionally, when a rider turns the seat tube 420, the rider's weightis shifted to one side of the tricycle 400. In response to the shift inweight, the joint 474 a, 474 b between the front portion 401 and rearportion 402 of the frame 413 at the hinge pins 472 gives to favor thedirection of steering indicated by the rider, additionally causing thetricycle 400 to lean into the turn. For example, if a rider desires toturn the tricycle 400 to the right by pushing on the left end of thehandlebar 438 and pulling on the right end of the handlebar 438 torotate the seat tube 420 within the head tube 428, an angle is createdbetween the orientation of the front wheel 404 a and the rear wheels 404b, 404 c, which are all normally parallel.

The angle between the front portion 401 and the rear portion 402 of thetricycle 400 thus causes the rider thereon to lean to the right and theweight of the rider shifts to the right side of the tricycle 400. Theweight of the rider on the right side causes the joint 474 a to flexdownward about the hinge pin 472 aiding in the turn. This downwardflexion places tension on the restraint chain 470 and on the flange 443of the fork extension 442 b on the left side of the tricycle 400 causingthe joint 474 b to flex upward about the hinge pin 472. The opposingdirections of flexion at the joints 474 a, 474 b also aids in turningthe tricycle 400. The rider can thus effect the sharpness of a turn bythe extent to which he shifts his weight.

The mechanical advantage drive system for the tricycle 400 is depictedin FIGS. 6-9. The drive system begins with a pair of pedals 446 attachedto a pair of crank arms 448 that extend from the bottom bracket 416. Thecrank arms 448 are attached to each end of a spindle (not shown) thatrotates within the bottom bracket 416. A chain ring 452 is attached tothe left side of the spindle. The chain ring 452 thus rotates with thespindle in the bottom bracket 416 as the rider pushes the pedals 446 ina circular motion.

The chain ring 452 has a plurality of teeth that extend from thecircumference of the chain rings 452. The teeth of the chain ring 452engage a front chain 462, which is a continuous loop that engages thefront hub 412 a to drive the front wheel 404 a. There may be more thanone chain ring 452; for example, there may be two or three chain ringsas commonly found on bicycles. A front derailleur (not shown) may beused to transfer the front chain 348 from one chain ring to another. Thefront hub 412 a includes a freewheel (not shown) to allow the hub tospin freely when the mechanical advantage drive takes over.

The front chain 462 connects the chain ring 452 to a drive sprocket 454attached to the front hub 412 a on the right side of the tricycle 400.Alternately, a plurality of sprockets, generally collected and attachedtogether as a cassette, may be attached to the front hub 412 a to drivethe front wheel 404 a. The front chain 462 engages the teeth of thedrive sprocket 454. If a cassette were used in place of the single drivesprocket 454, the front chain 462 may also be threaded through aderailleur (not shown) that moves the front chain 462 between thesprockets in the cassette.

A transfer ring 450 may also be attached to the right side of thespindle in the bottom bracket 416. The transfer ring 450 is also drivenby the rider pushing the pedals 446. The transfer ring 450 is toothedabout the circumference similar to the chain ring 452. A rear chain 464engages the transfer ring 450 and extends rearward along the inside ofthe right bottom tube 424 a as a continuous loop to drive the axle andthe pulley hub 426 mounted between the junction of the right and leftbottom tubes 424 a, 424 b and the rear down tubes 422 a, 422 b.

The rear chain 464 engages a pulley sprocket 456 fixed to the right sideof the axle. Alternately, a plurality of sprockets, generally collectedand attached together as a cassette, may be used in place of the singlepulley sprocket 456. A derailleur may be attached to the junction of therear down tubes 422 a, 422 b and the bottom tubes 424 a, 424 b and usedto shift between the sprockets in the pulley cassette.

A pulley 458 mounted on the pulley hub 426, which rotates about thespindle to the left of the pulley sprocket 456. The pulley hub 426 has afreewheel (not shown), similar to standard freewheels on rear wheels ofbicycles, mounted about the spindle. The freewheel is adapted to engagethe spindle, thus turning the pulley hub 426 and the attached pulley 458when the gearing is selected to engage the pulley 458. Alternately, thefreewheel freely rotates about the spindle when the gearing is directlydriving the front wheel 404 a. The pulley 458 may thus be turned byrotational transfer from the pulley sprocket 456 to the pulley hub 426.

The circumference of the pulley 458 is toothed to engage a belt 466 thatis used to additionally drive the front wheel 404 a. A drive rim 460 isattached to the front rim 408 a of the front wheel 404 a. The drive rim460 is toothed and engages the belt 466 driven by the pulley 458. Again,FIGS. 4 and 5 depict the construction of the drive rim in greaterdetail. The belt 466 may be made, for example, of reinforced rubber,toothed on one side for engaging the pulley 458 and drive rim 460 andflat on the other to minimize potential interference with the ground orcollection of dirt and grit due to the close proximity of the belt 466to the ground when traveling around the front wheel 404 a. Note thatsince mechanical advantage drive system of the tricycle 400 drives thefront wheel 404 a, the belt 466 pulls on the front wheel 404 a from thebottom in order to propel the tricycle 400 forward.

The freewheel in the pulley hub 426 allows the pulley 458 to spin freelyas the front wheel 404 a rotates the pulley 458 via the belt 466 fasterthan the gearing of the pulley sprocket 456 is rotated by the pull ofthe rear chain 464. The relationship between the gearing of the drivesprocket 454 and the pulley sprocket 456 is chosen such that the pulley458 engages the front wheel 404 a when the rear chain 464 rotates thepulley sprocket 456 at a faster speed than the front chain 462 rotatesthe drive sprocket 454. When the pulley 458 overtakes the drive sprocket454 as the drive for the front wheel 402 a, the freewheel in the fronthub 412 a spins freely. The front wheel 404 a is at this point driven bythe belt 466 through engagement with the drive rim 460.

The mechanical advantage achieved using the pulley 458 to drive thefront wheel 402 a of the tricycle 400 can be seen by comparing theconfiguration of the components of the tricycle 400 to the schematicdiagram of the cycle 200 in FIG. 2. The belt 466 engaging the frontwheel 402 a about the drive rim 460 continuously passes a point adjacentto a surface on which the front wheel 202 a of the tricycle 400 is incontact. Thus, an instantaneous fixed point on the belt 466 iscontinuously achieved. When the pulley 458 is engaged, a mechanicaladvantage is achieved through the combination of the instantaneous fixedend of the belt 466 and the force transfer across the pulley 458, thusdecreasing the force required of the rider on the rear chain 464 todrive the belt 466 and move the tricycle 400 forward.

An alternate implementation of a tricycle 500 with a mechanicaladvantage drive system is depicted in FIG. 11. The profile of thetricycle 500 is lower and provides increased aerodynamics. Toadditionally reduce aerodynamic drag or alternately provide weatherprotection, a fairing (not shown) may be mounted on the tricycle 500 toenvelop the rider. The tricycle 500 has a front wheel 504 a and two rearwheels 504 b attached to a frame 513. Each of the wheels 504 a, 504 bcomprises a hub 512 a, 512 b attached to a rim 508 a, 508 b, via a setof spokes 510. Tires 506 are mounted on each of the rims 508 a, 508 b.

A front portion 501 of the frame 513 is formed about a bottom bracket516, a front down tube 518, a seat tube 520, a pair of rear down tubes522, a pair of front bottom tubes 524 a, and a pair of rear bottom tubes524 b. The front down tube 518 and the rear down tubes 522 are eachattached at one end to an upper portion of the seat tube 520. The lowerend of the seat tube 520 is fixed to the bottom bracket 516. The rearbottom tubes 524 b are attached at a first end to the bottom bracket 516and at a second end to the lower ends of the rear down tubes 522. Apulley hub 526 rotates on an axel mounted between the junction of therear bottom tubes 524 b and the rear down tubes 522.

The lower end of the front down tube 518 connects with a front fork 514.The front bottom tubes 524 a are connected at a first end to the bottombracket 516 and extend forward to join the front fork 514 and connectwith and support an axle 511 in the front hub 512 a about which thefront wheel 504 a rotates.

A head tube 528 interfaces with the seat tube 520 allowing the seat tube520 to turn on a bearing interface (not shown) within the head tube 528.The seat tube 520 extends through the head tube 528 to support a seat530. A seat post (not shown) may fit within the seat tube 520 to allowthe height of the seat to be adjusted. A backrest bracket 532 may befixed to either the bottom of the seat 530 or the top of the seat postto hold a backrest 534 above and behind the seat 530 to support the backof a rider.

A pair of angled handlebar brackets 536 is fixed to the head tube 528.The handlebar brackets 536 extend rearward at angles toward the rightand left sides of the tricycle 500, respectively. The handlebar brackets536 form a triangle with the head tube 528 such that the two open endsof the angle are fixed to the head tube 528 and the vertex of the angleis attached to a handlebar 538.

The handlebar 538 may generally be a partial oval shape and extend fromunder the seat 530 to curve up adjacent to or over the lap of a riderwhen seated in the seat 530 from each side of the tricycle 500. Thegrips 539 of the handlebars 538 are available for easy grasping by therider to steer the tricycle 500 and aid in the balance of the riderwhile on the tricycle 500. The head tube 528, handlebar 538, andhandlebar brackets 536 function as the interface between the frontportion 501 of the frame 513 and a rear portion 502 of the frame 513,connecting the rear wheels 504 b to the rest of the tricycle 500.

As in the embodiment of FIGS. 6-10, this interface also functions as thesteering mechanism for the tricycle 500. A pair of suspension brackets540 may be flexibly or rotationally fixed to the handlebar 538 adjacentthe handlebar brackets 536, although the suspension brackets 540 may belocated elsewhere on the handlebar 538. In this implementation, eachsuspension bracket 540 comprises a plate to which a rear fork 544 ismounted. Each suspension bracket 540 that acts as a suspension for therear portion 502 of the tricycle 500 and may include a spring resistanceto further support the rear portion 502 of the tricycle 500. The rearwheels 504 b are mounted to the rear forks 544 by the axle of each rearhub 512 b.

The suspension brackets 540 are also attached to respective ends of arestraint chain 570 by pins 542. The suspension brackets 540 may have adownwardly extending flange to which the restraint chain 570 isattached. As previously described, such a flange can effectivelylengthen the travel of the restraint chain 570 to augment the flexion ofthe joint 572 between the front portion 501 and rear portion 502 of thetricycle 500 and thus augment the turning ability of the tricycle 500.

The restraint chain 570 wraps around a head sprocket 568 that is mountedat the top of the head tube 528. The head sprocket 568 may be formed ofa toothed sprocket mounted on a set of bearings that allow the headsprocket 568 to rotate around the head tube 528. In practice, the headsprocket 568 travels minimally as it is constrained by its engagementwith the restraint chain 570. The weight of the tricycle 500 and therider thereon push a joint 572 at the suspension brackets 540 againstthe restraint chain 570. The restraint chain 570 thus prevents the rearforks 544 from collapsing upward at the suspension brackets 540 underthe weight. The restraint chain 570 does allow for slight flex andmovement of the suspension brackets 540 during a turn.

The steering system of the tricycle 500 operates similarly to thesteering system of the implementation shown in FIGS. 6-9, i.e., thetricycle 500 is steered by a combination of turning the seat tube 520within the head tube 528 and flexing the joints 572 between the frontportion 501 and rear portion 502 of the frame 513. The rider holds ontothe handlebars 538 and, by shifting his body, the seat 530, attachedseat post 520, and thus the entire front portion 501 of the frame 513turn with respect to the head tube 528 and the attached rear portion 502of the tricycle 500. Additionally, when a rider turns the front portion501, the joint 572 between the front portion 501 and rear portion 502 ofthe frame 513 at the suspension brackets 540 bends to favor thedirection of steering indicated by the rider, additionally causing thetricycle 500 to lean into the turn.

The mechanical advantage drive system for the tricycle 500 includes apair of pedals 546 attached to a pair of crank arms 548 that extend fromthe bottom bracket 516. The crank arms 548 are attached to each end of aspindle (not shown) that rotates within the bottom bracket 516. A chainring 552 is attached to the left side of the spindle. The chain ring 552thus rotates with the spindle in the bottom bracket 516 as the riderpushes the pedals 546 in a circular motion.

The chain ring 552 has a plurality of teeth that extend from thecircumference of the chain rings 552. The teeth of the chain ring 552engage a front chain 562, which is a continuous loop that engages thefront hub 512 a to drive the front wheel 504 a. There may be more thanone chain ring 552; for example, there may be two or three chain ringsas commonly found on bicycles. A front derailleur (not shown) may beused to transfer the front chain 348 from one chain ring to another. Thefront hub 512 a includes a freewheel (not shown) to allow the hub tospin freely when the mechanical advantage drive takes over.

The front chain 562 connects the chain ring 552 to a plurality ofsprockets, generally collected and attached together as a drive cassette554 attached to the front hub 514 on the right side of the tricycle 500.Alternately, a single sprocket could be used instead of the drivecassette 554. The front chain 562 engages the teeth of the sprockets inthe drive cassette 554. The front chain 562 is also threaded through aderailleur 555 that moves the front chain 562 between the sprockets inthe drive cassette 554. Note that since the front wheel 502 a is beingdriven, the front chain 562 pulls downward and rearward on the sprocketsof the drive cassette 554, which is opposite the direction of pull bythe chain on the sprockets on a standard bicycle. Therefore, if using astandard derailleur mechanism, the derailleur 555 is mounted upside downat the front hub 512 a to provide tension to the slack in the upperportion of the front chain 562.

A transfer ring 550 may also be attached to the right side of thespindle in the bottom bracket 516. The transfer ring 550 is also drivenby the rider pushing the pedals 546. The transfer ring 550 is toothedabout the circumference similar to the chain ring 552. A rear chain 564engages the transfer ring 550 and extends rearward along the inside ofthe rear bottom tubes 524 b as a continuous loop to drive the pulleyaxle 527 and the pulley hub 526 mounted between the junction of the rearbottom tubes 524 b and the rear down tubes 522.

The rear chain 564 engages a plurality of sprockets, generally collectedand attached together as a pulley cassette 556 fixed to the right sideof the pulley axle 527. Alternately, a single sprocket may be used inplace of the pulley cassette 556. The rear chain 564 is threaded througha derailleur 557 attached to the junction of the rear down tubes 522 andthe rear bottom tubes 524 b, which is used to shift the rear chain 564between the sprockets in the pulley cassette 556.

A pulley 558 mounted on the pulley hub 526 rotates about the spindle tothe left of the pulley sprocket 556. The pulley hub 526 has a freewheel(not shown) adapted to engage the spindle, thus turning the pulley hub526 and the attached pulley 558 when the gearing is selected to engagethe pulley 558. Alternately, the freewheel freely rotates about thespindle when the gearing is directly driving the front wheel 504 a. Thepulley 558 may thus be turned by rotational transfer from the pulleysprocket 556 to the pulley hub 526.

The circumference of the pulley 558 is toothed to engage a belt 566 thatis used to additionally drive the front wheel 502 a. A drive rim 560 isattached to the front rim 508 a of the front wheel 502 a. The drive rim560 is toothed and engages the belt 566 driven by the pulley 558. Therelationship between the gearing of the drive system is similar to thedescription above with respect to FIGS. 6-9 and thus provides amechanical advantage to the rider. It may also be desirable to mount amotor to the frame at one of multiple locations to alternately power thetricycle and take advantage of the mechanical advantage drive system tocarry perhaps greater loads.

The above specification, examples, and data provide a completedescription of the structure and use of exemplary embodiments of theinvention. Although various embodiments of the invention have beendescribed above with a certain degree of particularity, or withreference to one or more individual embodiments, those skilled in theart could make numerous alterations to the disclosed embodiments withoutdeparting from the spirit or scope of this invention. Other embodimentsor implementations are therefore contemplated. It is intended that allmatter contained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative only of particularembodiments and not limiting. Changes in detail or structure may be madewithout departing from the basic elements of the invention as defined inthe following claims.

1. A cycle with a mechanical advantage drive system comprising a frame;a wheel rotationally attached to the frame; a drive rim attached to thewheel adjacent to an outer circumference of the wheel; a pulleyrotationally attached to the frame; a crank arm rotationally attached tothe frame and adapted to drive the pulley; and a belt that engages thepulley and the drive rim, wherein the belt drives the wheel when thecrank arm drives the pulley.
 2. The cycle of claim 1, wherein the pulleyfurther comprise a pulley hub through which the pulley is attached tothe frame; and wherein the cycle further comprises a transfer ringrotationally attached to the frame and fixed to the crank arm; a firstsprocket fixed to the pulley hub; and a first chain that engages thetransfer ring and the first sprocket, wherein the first chain drives thefirst sprocket when the crank arm rotates.
 3. The cycle of claim 2,wherein the wheel further comprises a wheel hub through which the wheelis attached to the frame; the wheel hub comprises a first freewheel; andthe pulley hub further comprises a second freewheel; and wherein thecycle further comprises a chain ring rotationally attached to the frameand fixed to the crank arm; a second sprocket fixed to the wheel hub;and a second chain that engages the chain ring and the second sprocket,wherein the second chain drives the second sprocket when the crank armrotates.
 4. A bicycle with a mechanical advantage drive systemcomprising a frame; a front wheel rotationally attached to the frame; arear wheel rotationally attached to the frame; a drive rim attached tothe rear wheel adjacent to an outer circumference of the rear wheel; apulley rotationally attached to the frame and positioned behind the rearwheel; a crank arm rotationally attached to the frame and adapted todrive the pulley; and a belt that engages the pulley and the drive rim,wherein the belt drives the rear wheel when the crank arm drives thepulley.
 5. The bicycle of claim 4, wherein the pulley further comprisesa pulley hub through which the pulley is attached to the frame; andwherein the bicycle further comprises a transfer ring rotationallyattached to the frame and fixed to the crank arm; a first sprocket fixedto the pulley hub; and a first chain that engages the transfer ring andthe first sprocket, wherein the first chain drives the first sprocketwhen the crank arm rotates.
 6. The bicycle of claim 5, wherein the rearwheel further comprises a wheel hub through which the rear wheel isattached to the frame; the wheel hub comprises a first freewheel; andthe pulley hub further comprises a second freewheel; and wherein thebicycle further comprises a chain ring rotationally attached to theframe and fixed to the crank arm; a second sprocket fixed to the wheelhub; and a second chain that engages the chain ring and the secondsprocket, wherein the second chain drives the second sprocket when thecrank arm rotates.
 7. The bicycle of claim 5 further comprising aderailleur attached to the frame adjacent the pulley hub; and whereinthe first sprocket comprises a cassette of a plurality of sprockets; thefirst chain is threaded through the derailleur; and the derailleurswitches engagement of the first chain between the plurality ofsprockets in the cassette.
 8. The bicycle of claim 6 further comprisinga derailleur attached to the frame adjacent the wheel hub; and whereinthe second sprocket comprises a cassette of a plurality of sprockets;the second chain is threaded through the derailleur; and the derailleurswitches engagement of the second chain between the plurality ofsprockets in the cassette.
 9. A tricycle with a mechanical advantagedrive system comprising a frame; a front wheel rotationally attached tothe frame; a first rear wheel rotationally attached to the frame; asecond rear wheel rotationally attached to the frame; a drive rimattached to the front wheel adjacent to an outer circumference of thefront wheel; a pulley rotationally attached to the frame and positionedbehind the front wheel; a crank arm rotationally attached to the frameand adapted to drive the pulley; and a belt that engages the pulley andthe drive rim, wherein the belt drives the front wheel when the crankarm drives the pulley.
 10. The tricycle of claim 9, wherein the pulleyfurther comprises a pulley hub through which the pulley is attached tothe frame; and wherein the tricycle further comprises a transfer ringrotationally attached to the frame and fixed to the crank arm; a firstsprocket fixed to the pulley hub; and a first chain that engages thetransfer ring and the first sprocket, wherein the first chain drives thefirst sprocket when the crank arm rotates.
 11. The tricycle of claim 10,wherein the front wheel further comprises a wheel hub through which thefront wheel is attached to the frame; the wheel hub comprises a firstfreewheel; and the pulley hub further comprises a second freewheel; andwherein the bicycle further comprises a chain ring rotationally attachedto the frame and fixed to the crank arm; a second sprocket fixed to thewheel hub; and a second chain that engages the chain ring and the secondsprocket, wherein the second chain drives the second sprocket when thecrank arm rotates.
 12. The tricycle of claim 10 further comprising aderailleur attached to the frame adjacent the pulley hub; and whereinthe first sprocket comprises a cassette of a plurality of sprockets; thefirst chain is threaded through the derailleur; and the derailleurswitches engagement of the first chain between the plurality ofsprockets in the cassette.
 13. The tricycle of claim 11 furthercomprising a derailleur attached to the frame adjacent the wheel hub;and wherein the second sprocket comprises a cassette of a plurality ofsprockets; the second chain is threaded through the derailleur; and thederailleur switches engagement of the second chain between the pluralityof sprockets in the cassette.
 14. The tricycle of claim 9, wherein theframe further comprises a front portion attached to the front wheel; aninterface portion rotationally attached to the front portion; and a rearportion hinged to the interface portion and attached to both the firstrear wheel and the second rear wheel.
 15. The tricycle of claim 15,wherein the front portion further comprises a seat tube that supports aseat; and the interface portion further comprises a head tube throughwhich the seat tube passes and within which the seat tube rotates. 16.The tricycle of claim 15, wherein the interface portion furthercomprises a handlebar attached to the head tube; the rear portionfurther comprises a first rear fork attached to the first rear wheel; asecond rear fork attached to the second rear wheel; and the first rearfork and the second rear fork are hinged to the handlebar.
 17. Thetricycle of claim 16 further comprising a sprocket rotationally mountedaround either the head tube or the seat tube; and a third chain attachedto the first rear fork at a first end, attached to the second rear forkat a second end, and engaged with the sprocket between the first end andthe second end.
 18. The tricycle of claim 17, wherein the first rearfork and the second rear fork each further comprise a flange extendingdownward from a position adjacent the hinge with the handlebar; and thefirst end of third chain and the second end of the third chain areattached to the respective flange.
 19. The tricycle of claim 15, whereinthe seat is supported by the seat tube above the head tube.
 20. Thetricycle of claim 19, wherein the handlebar extends upward from belowthe seat on each side of the seat.